Rollup of 5 pull requests

src/libcore/intrinsics.rs

@@ -1326,30 +1326,10 @@ extern "rust-intrinsic" {
     pub fn nontemporal_store<T>(ptr: *mut T, val: T);
 }
 
-mod real_intrinsics {
-  extern "rust-intrinsic" {
-    /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
-    /// and destination must *not* overlap.
-    /// For the full docs, see the stabilized wrapper [`copy_nonoverlapping`].
-    ///
-    /// [`copy_nonoverlapping`]: ../../std/ptr/fn.copy_nonoverlapping.html
-    pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
-
-    /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
-    /// and destination may overlap.
-    /// For the full docs, see the stabilized wrapper [`copy`].
-    ///
-    /// [`copy`]: ../../std/ptr/fn.copy.html
-    pub fn copy<T>(src: *const T, dst: *mut T, count: usize);
-
-    /// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
-    /// `val`.
-    /// For the full docs, see the stabilized wrapper [`write_bytes`].
-    ///
-    /// [`write_bytes`]: ../../std/ptr/fn.write_bytes.html
-    pub fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
-  }
-}
+// Some functions are defined here because they accidentally got made
+// available in this module on stable. See <https://github.com/rust-lang/rust/issues/15702>.
+// (`transmute` also falls into this category, but it cannot be wrapped due to the
+// check that `T` and `U` have the same size.)
 
 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
 /// and destination must *not* overlap.
@@ -1437,7 +1417,10 @@ mod real_intrinsics {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[inline]
 pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
-    real_intrinsics::copy_nonoverlapping(src, dst, count);
+    extern "rust-intrinsic" {
+        fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+    }
+    copy_nonoverlapping(src, dst, count);
 }
 
 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
@@ -1494,7 +1477,10 @@ pub unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[inline]
 pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
-    real_intrinsics::copy(src, dst, count)
+    extern "rust-intrinsic" {
+        fn copy<T>(src: *const T, dst: *mut T, count: usize);
+    }
+    copy(src, dst, count)
 }
 
 /// Sets `count * size_of::<T>()` bytes of memory starting at `dst` to
@@ -1572,7 +1558,10 @@ pub unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[inline]
 pub unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
-    real_intrinsics::write_bytes(dst, val, count)
+    extern "rust-intrinsic" {
+        fn write_bytes<T>(dst: *mut T, val: u8, count: usize);
+    }
+    write_bytes(dst, val, count)
 }
 
 // Simple bootstrap implementations of minnum/maxnum for stage0 compilation.

src/librustc/hir/lowering.rs

@@ -2168,7 +2168,7 @@ impl<'a> LoweringContext<'a> {
         itctx: ImplTraitContext<'_>,
         explicit_owner: Option<NodeId>,
     ) -> hir::PathSegment {
-        let (mut generic_args, infer_types) = if let Some(ref generic_args) = segment.args {
+        let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
             let msg = "parenthesized type parameters may only be used with a `Fn` trait";
             match **generic_args {
                 GenericArgs::AngleBracketed(ref data) => {
@@ -2230,17 +2230,17 @@ impl<'a> LoweringContext<'a> {
                 .collect();
             if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
                 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
-                let no_ty_args = generic_args.args.len() == expected_lifetimes;
+                let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
                 let no_bindings = generic_args.bindings.is_empty();
-                let (incl_angl_brckt, insertion_span, suggestion) = if no_ty_args && no_bindings {
+                let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
                     // If there are no (non-implicit) generic args or associated type
                     // bindings, our suggestion includes the angle brackets.
                     (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
                 } else {
                     // Otherwise (sorry, this is kind of gross) we need to infer the
                     // place to splice in the `'_, ` from the generics that do exist.
                     let first_generic_span = first_generic_span
-                        .expect("already checked that type args or bindings exist");
+                        .expect("already checked that non-lifetime args or bindings exist");
                     (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
                 };
                 match self.anonymous_lifetime_mode {
@@ -2263,7 +2263,7 @@ impl<'a> LoweringContext<'a> {
                             expected_lifetimes,
                             path_span,
                             incl_angl_brckt,
-                            insertion_span,
+                            insertion_sp,
                             suggestion,
                         );
                         err.emit();
@@ -2280,7 +2280,7 @@ impl<'a> LoweringContext<'a> {
                                 expected_lifetimes,
                                 path_span,
                                 incl_angl_brckt,
-                                insertion_span,
+                                insertion_sp,
                                 suggestion,
                             )
                         );
@@ -2305,7 +2305,7 @@ impl<'a> LoweringContext<'a> {
             Some(id),
             Some(self.lower_res(res)),
             generic_args,
-            infer_types,
+            infer_args,
         )
     }
 
@@ -2316,9 +2316,10 @@ impl<'a> LoweringContext<'a> {
         mut itctx: ImplTraitContext<'_>,
     ) -> (hir::GenericArgs, bool) {
         let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
-        let has_types = args.iter().any(|arg| match arg {
+        let has_non_lt_args = args.iter().any(|arg| match arg {
+            ast::GenericArg::Lifetime(_) => false,
             ast::GenericArg::Type(_) => true,
-            _ => false,
+            ast::GenericArg::Const(_) => true,
         });
         (
             hir::GenericArgs {
@@ -2328,7 +2329,7 @@ impl<'a> LoweringContext<'a> {
                     .collect(),
                 parenthesized: false,
             },
-            !has_types && param_mode == ParamMode::Optional
+            !has_non_lt_args && param_mode == ParamMode::Optional
         )
     }
 

src/librustc/hir/map/definitions.rs

@@ -582,9 +582,17 @@ impl DefPathData {
     }
 }
 
+/// Evaluates to the number of tokens passed to it.
+///
+/// Logarithmic counting: every one or two recursive expansions, the number of
+/// tokens to count is divided by two, instead of being reduced by one.
+/// Therefore, the recursion depth is the binary logarithm of the number of
+/// tokens to count, and the expanded tree is likewise very small.
 macro_rules! count {
-    () => (0usize);
-    ( $x:tt $($xs:tt)* ) => (1usize + count!($($xs)*));
+    ()                     => (0usize);
+    ($one:tt)              => (1usize);
+    ($($pairs:tt $_p:tt)*) => (count!($($pairs)*) << 1usize);
+    ($odd:tt $($rest:tt)*) => (count!($($rest)*) | 1usize);
 }
 
 // We define the GlobalMetaDataKind enum with this macro because we want to

src/librustc/hir/mod.rs

@@ -348,7 +348,7 @@ pub struct PathSegment {
     /// This only applies to expression and pattern paths, and
     /// out of those only the segments with no type parameters
     /// to begin with, e.g., `Vec::new` is `<Vec<..>>::new::<..>`.
-    pub infer_types: bool,
+    pub infer_args: bool,
 }
 
 impl PathSegment {
@@ -358,7 +358,7 @@ impl PathSegment {
             ident,
             hir_id: None,
             res: None,
-            infer_types: true,
+            infer_args: true,
             args: None,
         }
     }
@@ -368,13 +368,13 @@ impl PathSegment {
         hir_id: Option<HirId>,
         res: Option<Res>,
         args: GenericArgs,
-        infer_types: bool,
+        infer_args: bool,
     ) -> Self {
         PathSegment {
             ident,
             hir_id,
             res,
-            infer_types,
+            infer_args,
             args: if args.is_empty() {
                 None
             } else {

src/librustc/hir/print.rs

@@ -1196,7 +1196,7 @@ impl<'a> State<'a> {
 
         segment.with_generic_args(|generic_args| {
             if !generic_args.args.is_empty() || !generic_args.bindings.is_empty() {
-                return self.print_generic_args(&generic_args, segment.infer_types, true);
+                return self.print_generic_args(&generic_args, segment.infer_args, true);
             }
             Ok(())
         })?;
@@ -1561,7 +1561,7 @@ impl<'a> State<'a> {
             if segment.ident.name != kw::PathRoot {
                self.print_ident(segment.ident)?;
                segment.with_generic_args(|generic_args| {
-                   self.print_generic_args(generic_args, segment.infer_types,
+                   self.print_generic_args(generic_args, segment.infer_args,
                                            colons_before_params)
                })?;
             }
@@ -1574,7 +1574,7 @@ impl<'a> State<'a> {
         if segment.ident.name != kw::PathRoot {
            self.print_ident(segment.ident)?;
            segment.with_generic_args(|generic_args| {
-               self.print_generic_args(generic_args, segment.infer_types, false)
+               self.print_generic_args(generic_args, segment.infer_args, false)
            })?;
         }
         Ok(())
@@ -1602,7 +1602,7 @@ impl<'a> State<'a> {
                         self.print_ident(segment.ident)?;
                         segment.with_generic_args(|generic_args| {
                             self.print_generic_args(generic_args,
-                                                    segment.infer_types,
+                                                    segment.infer_args,
                                                     colons_before_params)
                         })?;
                     }
@@ -1614,7 +1614,7 @@ impl<'a> State<'a> {
                 self.print_ident(item_segment.ident)?;
                 item_segment.with_generic_args(|generic_args| {
                     self.print_generic_args(generic_args,
-                                            item_segment.infer_types,
+                                            item_segment.infer_args,
                                             colons_before_params)
                 })
             }
@@ -1626,7 +1626,7 @@ impl<'a> State<'a> {
                 self.print_ident(item_segment.ident)?;
                 item_segment.with_generic_args(|generic_args| {
                     self.print_generic_args(generic_args,
-                                            item_segment.infer_types,
+                                            item_segment.infer_args,
                                             colons_before_params)
                 })
             }
@@ -1635,7 +1635,7 @@ impl<'a> State<'a> {
 
     fn print_generic_args(&mut self,
                              generic_args: &hir::GenericArgs,
-                             infer_types: bool,
+                             infer_args: bool,
                              colons_before_params: bool)
                              -> io::Result<()> {
         if generic_args.parenthesized {
@@ -1681,7 +1681,7 @@ impl<'a> State<'a> {
 
             // FIXME(eddyb): this would leak into error messages (e.g.,
             // "non-exhaustive patterns: `Some::<..>(_)` not covered").
-            if infer_types && false {
+            if infer_args && false {
                 start_or_comma(self)?;
                 self.s.word("..")?;
             }

src/librustc_interface/util.rs

@@ -121,9 +121,13 @@ pub fn create_session(
 }
 
 // Temporarily have stack size set to 32MB to deal with various crates with long method
-// chains or deep syntax trees.
+// chains or deep syntax trees, except when on Haiku.
 // FIXME(oli-obk): get https://github.com/rust-lang/rust/pull/55617 the finish line
-const STACK_SIZE: usize = 32 * 1024 * 1024; // 32MB
+#[cfg(not(target_os = "haiku"))]
+const STACK_SIZE: usize = 32 * 1024 * 1024;
+
+#[cfg(target_os = "haiku")]
+const STACK_SIZE: usize = 16 * 1024 * 1024;
 
 fn get_stack_size() -> Option<usize> {
     // FIXME: Hacks on hacks. If the env is trying to override the stack size

src/librustc_typeck/astconv.rs

@@ -13,7 +13,7 @@ use crate::middle::resolve_lifetime as rl;
 use crate::namespace::Namespace;
 use rustc::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
 use rustc::traits;
-use rustc::ty::{self, DefIdTree, Ty, TyCtxt, ToPredicate, TypeFoldable};
+use rustc::ty::{self, DefIdTree, Ty, TyCtxt, Const, ToPredicate, TypeFoldable};
 use rustc::ty::{GenericParamDef, GenericParamDefKind};
 use rustc::ty::subst::{Kind, Subst, InternalSubsts, SubstsRef};
 use rustc::ty::wf::object_region_bounds;
@@ -49,18 +49,23 @@ pub trait AstConv<'gcx, 'tcx> {
                                  -> &'tcx ty::GenericPredicates<'tcx>;
 
     /// Returns the lifetime to use when a lifetime is omitted (and not elided).
-    fn re_infer(&self, span: Span, _def: Option<&ty::GenericParamDef>)
+    fn re_infer(
+        &self,
+        param: Option<&ty::GenericParamDef>,
+        span: Span,
+    )
                 -> Option<ty::Region<'tcx>>;
 
     /// Returns the type to use when a type is omitted.
-    fn ty_infer(&self, span: Span) -> Ty<'tcx>;
+    fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
 
-    /// Same as `ty_infer`, but with a known type parameter definition.
-    fn ty_infer_for_def(&self,
-                        _def: &ty::GenericParamDef,
-                        span: Span) -> Ty<'tcx> {
-        self.ty_infer(span)
-    }
+    /// Returns the const to use when a const is omitted.
+    fn ct_infer(
+        &self,
+        ty: Ty<'tcx>,
+        param: Option<&ty::GenericParamDef>,
+        span: Span,
+    ) -> &'tcx Const<'tcx>;
 
     /// Projecting an associated type from a (potentially)
     /// higher-ranked trait reference is more complicated, because of
@@ -156,7 +161,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             }
 
             None => {
-                self.re_infer(lifetime.span, def)
+                self.re_infer(def, lifetime.span)
                     .unwrap_or_else(|| {
                         // This indicates an illegal lifetime
                         // elision. `resolve_lifetime` should have
@@ -191,7 +196,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 span,
                 def_id,
                 generic_args,
-                item_segment.infer_types,
+                item_segment.infer_args,
                 None,
             )
         });
@@ -208,7 +213,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
         seg: &hir::PathSegment,
         generics: &ty::Generics,
     ) -> bool {
-        let explicit = !seg.infer_types;
+        let explicit = !seg.infer_args;
         let impl_trait = generics.params.iter().any(|param| match param.kind {
             ty::GenericParamDefKind::Type {
                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait), ..
@@ -259,7 +264,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 GenericArgPosition::Value
             },
             def.parent.is_none() && def.has_self, // `has_self`
-            seg.infer_types || suppress_mismatch, // `infer_types`
+            seg.infer_args || suppress_mismatch, // `infer_args`
         ).0
     }
 
@@ -272,15 +277,14 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
         args: &hir::GenericArgs,
         position: GenericArgPosition,
         has_self: bool,
-        infer_types: bool,
+        infer_args: bool,
     ) -> (bool, Option<Vec<Span>>) {
         // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
         // that lifetimes will proceed types. So it suffices to check the number of each generic
         // arguments in order to validate them with respect to the generic parameters.
         let param_counts = def.own_counts();
         let arg_counts = args.own_counts();
         let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
-        let infer_consts = position != GenericArgPosition::Type && arg_counts.consts == 0;
 
         let mut defaults: ty::GenericParamCount = Default::default();
         for param in &def.params {
@@ -333,7 +337,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 offset
             );
             // We enforce the following: `required` <= `provided` <= `permitted`.
-            // For kinds without defaults (i.e., lifetimes), `required == permitted`.
+            // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
             // For other kinds (i.e., types), `permitted` may be greater than `required`.
             if required <= provided && provided <= permitted {
                 return (reported_late_bound_region_err.unwrap_or(false), None);
@@ -404,7 +408,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             );
         }
         // FIXME(const_generics:defaults)
-        if !infer_consts || arg_counts.consts > param_counts.consts {
+        if !infer_args || arg_counts.consts > param_counts.consts {
             check_kind_count(
                 "const",
                 param_counts.consts,
@@ -414,7 +418,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             );
         }
         // Note that type errors are currently be emitted *after* const errors.
-        if !infer_types
+        if !infer_args
             || arg_counts.types > param_counts.types - defaults.types - has_self as usize {
             check_kind_count(
                 "type",
@@ -511,7 +515,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             }
 
             // Check whether this segment takes generic arguments and the user has provided any.
-            let (generic_args, infer_types) = args_for_def_id(def_id);
+            let (generic_args, infer_args) = args_for_def_id(def_id);
 
             let mut args = generic_args.iter().flat_map(|generic_args| generic_args.args.iter())
                 .peekable();
@@ -535,7 +539,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                             | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
                                 // We expected a lifetime argument, but got a type or const
                                 // argument. That means we're inferring the lifetimes.
-                                substs.push(inferred_kind(None, param, infer_types));
+                                substs.push(inferred_kind(None, param, infer_args));
                                 params.next();
                             }
                             (_, _) => {
@@ -556,7 +560,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                     (None, Some(&param)) => {
                         // If there are fewer arguments than parameters, it means
                         // we're inferring the remaining arguments.
-                        substs.push(inferred_kind(Some(&substs), param, infer_types));
+                        substs.push(inferred_kind(Some(&substs), param, infer_args));
                         args.next();
                         params.next();
                     }
@@ -592,7 +596,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
         span: Span,
         def_id: DefId,
         generic_args: &'a hir::GenericArgs,
-        infer_types: bool,
+        infer_args: bool,
         self_ty: Option<Ty<'tcx>>)
         -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'tcx>>, Option<Vec<Span>>)
     {
@@ -617,7 +621,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             &generic_args,
             GenericArgPosition::Type,
             has_self,
-            infer_types,
+            infer_args,
         );
 
         let is_object = self_ty.map_or(false, |ty| {
@@ -644,7 +648,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             self_ty.is_some(),
             self_ty,
             // Provide the generic args, and whether types should be inferred.
-            |_| (Some(generic_args), infer_types),
+            |_| (Some(generic_args), infer_args),
             // Provide substitutions for parameters for which (valid) arguments have been provided.
             |param, arg| {
                 match (&param.kind, arg) {
@@ -661,11 +665,11 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 }
             },
             // Provide substitutions for parameters for which arguments are inferred.
-            |substs, param, infer_types| {
+            |substs, param, infer_args| {
                 match param.kind {
                     GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
                     GenericParamDefKind::Type { has_default, .. } => {
-                        if !infer_types && has_default {
+                        if !infer_args && has_default {
                             // No type parameter provided, but a default exists.
 
                             // If we are converting an object type, then the
@@ -693,22 +697,29 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                                        .subst_spanned(tcx, substs.unwrap(), Some(span))
                                 ).into()
                             }
-                        } else if infer_types {
+                        } else if infer_args {
                             // No type parameters were provided, we can infer all.
-                            if !default_needs_object_self(param) {
-                                self.ty_infer_for_def(param, span).into()
+                            let param = if !default_needs_object_self(param) {
+                                Some(param)
                             } else {
-                                self.ty_infer(span).into()
-                            }
+                                None
+                            };
+                            self.ty_infer(param, span).into()
                         } else {
                             // We've already errored above about the mismatch.
                             tcx.types.err.into()
                         }
                     }
                     GenericParamDefKind::Const => {
                         // FIXME(const_generics:defaults)
-                        // We've already errored above about the mismatch.
-                        tcx.consts.err.into()
+                        if infer_args {
+                            // No const parameters were provided, we can infer all.
+                            let ty = tcx.at(span).type_of(param.def_id);
+                            self.ct_infer(ty, Some(param), span).into()
+                        } else {
+                            // We've already errored above about the mismatch.
+                            tcx.consts.err.into()
+                        }
                     }
                 }
             },
@@ -880,7 +891,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
             self.create_substs_for_ast_path(span,
                                             trait_def_id,
                                             generic_args,
-                                            trait_segment.infer_types,
+                                            trait_segment.infer_args,
                                             Some(self_ty))
         })
     }
@@ -1428,7 +1439,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 if tcx.named_region(lifetime.hir_id).is_some() {
                     self.ast_region_to_region(lifetime, None)
                 } else {
-                    self.re_infer(span, None).unwrap_or_else(|| {
+                    self.re_infer(None, span).unwrap_or_else(|| {
                         span_err!(tcx.sess, span, E0228,
                             "the lifetime bound for this object type cannot be deduced \
                              from context; please supply an explicit bound");
@@ -2122,7 +2133,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 // values in a ExprKind::Closure, or as
                 // the type of local variables. Both of these cases are
                 // handled specially and will not descend into this routine.
-                self.ty_infer(ast_ty.span)
+                self.ty_infer(None, ast_ty.span)
             }
             hir::TyKind::CVarArgs(lt) => {
                 let va_list_did = match tcx.lang_items().va_list() {

src/librustc_typeck/check/closure.rs

@@ -598,7 +598,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
         let supplied_return = match decl.output {
             hir::Return(ref output) => astconv.ast_ty_to_ty(&output),
-            hir::DefaultReturn(_) => astconv.ty_infer(decl.output.span()),
+            hir::DefaultReturn(_) => astconv.ty_infer(None, decl.output.span()),
         };
 
         let result = ty::Binder::bind(self.tcx.mk_fn_sig(

src/librustc_typeck/check/mod.rs

@@ -100,11 +100,12 @@ use rustc_data_structures::indexed_vec::Idx;
 use rustc_target::spec::abi::Abi;
 use rustc::infer::opaque_types::OpaqueTypeDecl;
 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use rustc::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc::middle::region;
 use rustc::mir::interpret::{ConstValue, GlobalId};
 use rustc::traits::{self, ObligationCause, ObligationCauseCode, TraitEngine};
 use rustc::ty::{
-    self, AdtKind, CanonicalUserType, Ty, TyCtxt, GenericParamDefKind, Visibility,
+    self, AdtKind, CanonicalUserType, Ty, TyCtxt, Const, GenericParamDefKind, Visibility,
     ToPolyTraitRef, ToPredicate, RegionKind, UserType
 };
 use rustc::ty::adjustment::{
@@ -1938,29 +1939,49 @@ impl<'a, 'gcx, 'tcx> AstConv<'gcx, 'tcx> for FnCtxt<'a, 'gcx, 'tcx> {
         })
     }
 
-    fn re_infer(&self, span: Span, def: Option<&ty::GenericParamDef>)
-                -> Option<ty::Region<'tcx>> {
+    fn re_infer(
+        &self,
+        def: Option<&ty::GenericParamDef>,
+        span: Span,
+    ) -> Option<ty::Region<'tcx>> {
         let v = match def {
             Some(def) => infer::EarlyBoundRegion(span, def.name),
             None => infer::MiscVariable(span)
         };
         Some(self.next_region_var(v))
     }
 
-    fn ty_infer(&self, span: Span) -> Ty<'tcx> {
-        self.next_ty_var(TypeVariableOrigin {
-            kind: TypeVariableOriginKind::TypeInference,
-            span,
-        })
+    fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
+        if let Some(param) = param {
+            if let UnpackedKind::Type(ty) = self.var_for_def(span, param).unpack() {
+                return ty;
+            }
+            unreachable!()
+        } else {
+            self.next_ty_var(TypeVariableOrigin {
+                kind: TypeVariableOriginKind::TypeInference,
+                span,
+            })
+        }
     }
 
-    fn ty_infer_for_def(&self,
-                        ty_param_def: &ty::GenericParamDef,
-                        span: Span) -> Ty<'tcx> {
-        if let UnpackedKind::Type(ty) = self.var_for_def(span, ty_param_def).unpack() {
-            return ty;
+    fn ct_infer(
+        &self,
+        ty: Ty<'tcx>,
+        param: Option<&ty::GenericParamDef>,
+        span: Span,
+    ) -> &'tcx Const<'tcx> {
+        if let Some(param) = param {
+            if let UnpackedKind::Const(ct) = self.var_for_def(span, param).unpack() {
+                return ct;
+            }
+            unreachable!()
+        } else {
+            self.next_const_var(ty, ConstVariableOrigin {
+                kind: ConstVariableOriginKind::ConstInference,
+                span,
+            })
         }
-        unreachable!()
     }
 
     fn projected_ty_from_poly_trait_ref(&self,
@@ -5419,10 +5440,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     if !infer_args_for_err.contains(&index) {
                         // Check whether the user has provided generic arguments.
                         if let Some(ref data) = segments[index].args {
-                            return (Some(data), segments[index].infer_types);
+                            return (Some(data), segments[index].infer_args);
                         }
                     }
-                    return (None, segments[index].infer_types);
+                    return (None, segments[index].infer_args);
                 }
 
                 (None, true)
@@ -5443,13 +5464,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 }
             },
             // Provide substitutions for parameters for which arguments are inferred.
-            |substs, param, infer_types| {
+            |substs, param, infer_args| {
                 match param.kind {
                     GenericParamDefKind::Lifetime => {
-                        self.re_infer(span, Some(param)).unwrap().into()
+                        self.re_infer(Some(param), span).unwrap().into()
                     }
                     GenericParamDefKind::Type { has_default, .. } => {
-                        if !infer_types && has_default {
+                        if !infer_args && has_default {
                             // If we have a default, then we it doesn't matter that we're not
                             // inferring the type arguments: we provide the default where any
                             // is missing.

src/librustc_typeck/collect.rs

@@ -26,7 +26,7 @@ use rustc::ty::subst::{Subst, InternalSubsts};
 use rustc::ty::util::Discr;
 use rustc::ty::util::IntTypeExt;
 use rustc::ty::subst::UnpackedKind;
-use rustc::ty::{self, AdtKind, DefIdTree, ToPolyTraitRef, Ty, TyCtxt};
+use rustc::ty::{self, AdtKind, DefIdTree, ToPolyTraitRef, Ty, TyCtxt, Const};
 use rustc::ty::{ReprOptions, ToPredicate};
 use rustc::util::captures::Captures;
 use rustc::util::nodemap::FxHashMap;
@@ -47,7 +47,7 @@ use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc::hir::GenericParamKind;
 use rustc::hir::{self, CodegenFnAttrFlags, CodegenFnAttrs, Unsafety};
 
-use errors::Applicability;
+use errors::{Applicability, DiagnosticId};
 
 use std::iter;
 
@@ -186,24 +186,39 @@ impl<'a, 'tcx> AstConv<'tcx, 'tcx> for ItemCtxt<'a, 'tcx> {
 
     fn re_infer(
         &self,
-        _span: Span,
-        _def: Option<&ty::GenericParamDef>,
+        _: Option<&ty::GenericParamDef>,
+        _: Span,
     ) -> Option<ty::Region<'tcx>> {
         None
     }
 
-    fn ty_infer(&self, span: Span) -> Ty<'tcx> {
-        struct_span_err!(
-            self.tcx().sess,
+    fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
+        self.tcx().sess.struct_span_err_with_code(
             span,
-            E0121,
-            "the type placeholder `_` is not allowed within types on item signatures"
+            "the type placeholder `_` is not allowed within types on item signatures",
+            DiagnosticId::Error("E0121".into()),
         ).span_label(span, "not allowed in type signatures")
          .emit();
 
         self.tcx().types.err
     }
 
+    fn ct_infer(
+        &self,
+        _: Ty<'tcx>,
+        _: Option<&ty::GenericParamDef>,
+        span: Span,
+    ) -> &'tcx Const<'tcx> {
+        self.tcx().sess.struct_span_err_with_code(
+            span,
+            "the const placeholder `_` is not allowed within types on item signatures",
+            DiagnosticId::Error("E0121".into()),
+        ).span_label(span, "not allowed in type signatures")
+         .emit();
+
+        self.tcx().consts.err
+    }
+
     fn projected_ty_from_poly_trait_ref(
         &self,
         span: Span,

src/librustc_typeck/error_codes.rs

@@ -1482,8 +1482,8 @@ impl <'a> Drop for MyWrapper<'a> {
 "##,
 
 E0121: r##"
-In order to be consistent with Rust's lack of global type inference, type
-placeholders are disallowed by design in item signatures.
+In order to be consistent with Rust's lack of global type inference,
+type and const placeholders are disallowed by design in item signatures.
 
 Examples of this error include:
 

src/libserialize/serialize.rs

@@ -723,10 +723,17 @@ macro_rules! peel {
     ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
 }
 
-/// Evaluates to the number of identifiers passed to it, for example: `count_idents!(a, b, c) == 3
-macro_rules! count_idents {
-    () => { 0 };
-    ($_i:ident, $($rest:ident,)*) => { 1 + count_idents!($($rest,)*) }
+/// Evaluates to the number of tokens passed to it.
+///
+/// Logarithmic counting: every one or two recursive expansions, the number of
+/// tokens to count is divided by two, instead of being reduced by one.
+/// Therefore, the recursion depth is the binary logarithm of the number of
+/// tokens to count, and the expanded tree is likewise very small.
+macro_rules! count {
+    ()                     => (0usize);
+    ($one:tt)              => (1usize);
+    ($($pairs:tt $_p:tt)*) => (count!($($pairs)*) << 1usize);
+    ($odd:tt $($rest:tt)*) => (count!($($rest)*) | 1usize);
 }
 
 macro_rules! tuple {
@@ -735,7 +742,7 @@ macro_rules! tuple {
         impl<$($name:Decodable),*> Decodable for ($($name,)*) {
             #[allow(non_snake_case)]
             fn decode<D: Decoder>(d: &mut D) -> Result<($($name,)*), D::Error> {
-                let len: usize = count_idents!($($name,)*);
+                let len: usize = count!($($name)*);
                 d.read_tuple(len, |d| {
                     let mut i = 0;
                     let ret = ($(d.read_tuple_arg({ i+=1; i-1 }, |d| -> Result<$name, D::Error> {

src/test/ui/const-generics/array-wrapper-struct-ctor.rs

@@ -0,0 +1,15 @@
+// run-pass
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct ArrayStruct<T, const N: usize> {
+    data: [T; N],
+}
+
+struct ArrayTuple<T, const N: usize>([T; N]);
+
+fn main() {
+    let _ = ArrayStruct { data: [0u32; 8] };
+    let _ = ArrayTuple([0u32; 8]);
+}

src/test/ui/const-generics/array-wrapper-struct-ctor.stderr

@@ -0,0 +1,6 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/array-wrapper-struct-ctor.rs:3:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+

src/test/ui/const-generics/derive-debug-array-wrapper.rs

@@ -0,0 +1,9 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+#[derive(Debug)]
+struct X<const N: usize> {
+    a: [u32; N], //~ ERROR `[u32; _]` doesn't implement `std::fmt::Debug`
+}
+
+fn main() {}

src/test/ui/const-generics/derive-debug-array-wrapper.stderr

@@ -0,0 +1,19 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/derive-debug-array-wrapper.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+
+error[E0277]: `[u32; _]` doesn't implement `std::fmt::Debug`
+  --> $DIR/derive-debug-array-wrapper.rs:6:5
+   |
+LL |     a: [u32; N],
+   |     ^^^^^^^^^^^ `[u32; _]` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
+   |
+   = help: the trait `std::fmt::Debug` is not implemented for `[u32; _]`
+   = note: required because of the requirements on the impl of `std::fmt::Debug` for `&[u32; _]`
+   = note: required for the cast to the object type `dyn std::fmt::Debug`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.